Abstract

Simulations of the Martian upper atmosphere have been conducted with ‘MarTIM’, University College
London’s Martian thermosphere and ionosphere general circulation model (GCM). MarTIM, a finite
difference model, solves the coupled non-linear Navier-Stokes equations of continuity and momentum as
well as an energy equation with calculations conducted on a fixed co-rotating grid of variable size in the
pressure coordinate system. From its lower boundary of 0.883 Pa (~60 km) to its upper boundary of
9.9×10−8 Pa (~200−350 km), it evaluates the main sources of solar forcing (EUV/UV and IR absorption)
while self-consistently determining the composition of four of the major gas species, CO2, N2, CO and
O. These four major gases are mutually diffused throughout the model in a typical run.
Development of MarTIM includes a consideration of the importance of neutral species diffusion
and advection on the thermodynamics of the modelled Martian atmosphere. The influence on the
modelled atmosphere of including additional neutral species is investigated. Next, a new infrared heating
parameterization has been introduced from background research of detailed non-LTE modelling. This has
allowed MarTIM to study thermospheric polar warming features as found in Mars Odyssey accelerometer
data.
MarTIM’s lower boundary is coupled to the Mars Climate Database (MCD v4.3) developed by the
University of Oxford, the Open University and Laboratoire de Météorologie Dynamique. This database
of GCM results provides MarTIM a physically self-consistent lower boundary derived from multiple
runs of the aforementioned circulation models. Consequently the effects of dust storms, non-migrating
tides and the influence of Martian topography are studied by prescription of MarTIM’s lower boundary.
MarTIM is also compared against density and temperature measurements derived from SPICAM stellar
occultation profiles.
Lastly, a new ionospheric code has been developed through collaboration with Laboratoire de Planétologie
de Grenoble. This has provided a more sophisticated ionosphere model that solves a one-dimensional
kinetic Boltzmann transport equation for the suprathermal population of electrons present in the Martian
ionosphere. MarTIM can now self-consistently describe an ionosphere produced by both primary
(photoionisation) and secondary ionisation (suprathermal electron propagation). This new ionospheric
model has been used to study the variation in secondary ionization efficiency (ratio of secondary to
primary ion production) through a large range of seasonal and solar conditions.

Type:

Thesis
(Doctoral)

Title:

Studies of the Martian upper atmosphere with the
UCL Mars thermosphere and ionosphere general
circulation model